After a fair bit of Googling and reading around, I'm none the wiser
about exactly how Linux 2.6.x sets the processor VID (or for that matter
how it decides the FID settings) when using the ondemand governor and
cpufreq stuff.
Can anyone tell me a) whether this is obtained from the BIOS, something
in the MSR of the processor or elsewhere and b) whether there is an
interface in /proc or /sys where one can find out what is set and modify it?
I'm not subscribed to the list so a Cc: would be appreciated, cheers!
--
Brian Morrison
[email protected]
Pallipadi, Venkatesh wrote:
>> After a fair bit of Googling and reading around, I'm none the wiser
>> about exactly how Linux 2.6.x sets the processor VID (or for
>> that matter
>> how it decides the FID settings) when using the ondemand governor and
>> cpufreq stuff.
>>
>> Can anyone tell me a) whether this is obtained from the BIOS,
>> something
>> in the MSR of the processor or elsewhere and
>
> Yes. The freq and voltage supported comes from the platform BIOS. BIOS
> exports this in an ACPI table which is handled by acpi-cpufreq driver in
> Linux kernel.
>
OK, thanks for that.
>
>> b) whether there is an
>> interface in /proc or /sys where one can find out what is set
>> and modify it?
>
> There is no way of modifying and using new VIDs etc in Linux kernel
> (other than exporting your own DSDT and hacking the related code).
Is there a way of viewing the ACPI table contents relating to the VIDs
and FIDs?
--
Brian Morrison
[email protected]
Brian Morrison wrote:
> Pallipadi, Venkatesh wrote:
>
>>> After a fair bit of Googling and reading around, I'm none the wiser
>>> about exactly how Linux 2.6.x sets the processor VID (or for that
>>> matter how it decides the FID settings) when using the ondemand
>>> governor and cpufreq stuff.
>>>
>>> Can anyone tell me a) whether this is obtained from the BIOS,
>>> something in the MSR of the processor or elsewhere and
>>
>> Yes. The freq and voltage supported comes from the platform BIOS. BIOS
>> exports this in an ACPI table which is handled by acpi-cpufreq driver in
>> Linux kernel.
>>
>
> OK, thanks for that.
>
>>
>>> b) whether there is an interface in /proc or /sys where one can find
>>> out what is set and modify it?
>>
>> There is no way of modifying and using new VIDs etc in Linux kernel
>> (other than exporting your own DSDT and hacking the related code).
>
> Is there a way of viewing the ACPI table contents relating to the VIDs
> and FIDs?
Viewing the decompiled ACPI DSDT may provide some hints, however the
kernel itself knows nothing about VID/FID settings for acpi-cpufreq,
basically the kernel writes to magic ACPI registers and the BIOS or
hardware take over to do what's required..